What if some huge, physically overpowering people held you captive and did painful things to you each day? What if they made fun of you when you screamed out of fear, cursed you for no reason, and threw you—literally threw you—back into a cage when they were finished roughing you up? Wouldn't you freeze in terror every time the door opened? Heart racing, you might wish to be invisible to your captors, but you never would be. The anxiety alone would be almost unbearable. It sounds like a nightmare, doesn't it? It is, and it's what monkeys endure in this and other laboratories every day.